Friction lining for wet running

ABSTRACT

A friction lining for wet running consists of a fabric which can be applied to a carrier ( 6 ) and is partly impregnated with resin. In order to provide favorable friction conditions it is proposed that the porosity of the fabric ( 1 ) impregnated with resin is higher in the zone of the friction face ( 4 ) by a lower resin content in a surface layer (h) than in the remaining layer.

BACKGROUND OF THE INVENTION

[0001] The invention relates to a friction lining for wet running,consisting of a fabric which can be applied to a carrier and is partlyimpregnated with resin, as well as to a method for producing such afriction lining.

DESCRIPTION OF THE PRIOR ART

[0002] In order to achieve an advantageous porosity for receiving andconducting the respectively used lubricating liquid in the case offriction linings made of a fabric consisting of carbon fibers and partlyimpregnated with resin, it is known (U.S. Pat. No. 5,662,993 A) to limitthe resin share to 18 to 40%. Despite this limitation of the resinshare, comparably high hydrodynamic friction shares are obtained whichreduce the coefficient of friction because the hardening of suchfriction linings occurs in heating presses which produce a resinaccumulation in the surface region in order to reduce theiroperationally induced settling tendency, which can lead to surfaceregions with a substantially coherent resin film which allows the localbuild-up of a hydrodynamic lubricant film in the zone of the laterfriction face. Despite the pressing of the friction linings during thehardening of the resin, the porosity of the friction linings requiredfor taking up the lubricating liquid produces a setting of the frictionlinings which progresses over the service life due to the operationallyinduced pressure strains, which entails a reduction of the pore volume.This setting inclination increases with decreasing resin content, sothat the resin content should be increased for reducing the settingbehavior of such a friction lining. This is contrary to the demand for asufficient porosity of the friction lining for receiving lubricatingliquid.

SUMMARY OF THE INVENTION

[0003] The invention is thus based on the object of providing a frictionlining of the kind mentioned above in such a way that on the one handthe demand for the lowest possible hydrodynamic friction share can befulfilled, and on the other hand the setting tendency can be reduced asfar as possible.

[0004] The invention achieves the object in such a way that the porosityof the fabric impregnated with resin is higher in the zone of thefriction face by a lower resin content in a surface layer than in theremaining layer.

[0005] The invention is based on the finding that the relatively highporosity which is relevant for the frictional behavior merely needs tobe ensured in a surface layer of the friction face. The porosity of theremaining layer of the friction lining, however, hardly plays any rolefor the frictional behavior at all. This means that at a comparably highshare of resin and the thus resulting lower porosity, a favorablefrictional behavior can be achieved when a sufficiently high porosity ina surface layer is striven for by a respectively lower resin content. Asa result of this measure, the otherwise mutually contradictingrequirements of a favorable discharge of the lubricating liquid by thefriction face and of the lowest possible setting behavior can befulfilled in an advantageous manner. It was noticed surprisingly thatneither the higher resin content with the thus resulting lower porosityof the friction lining outside of the surface layer of the frictionlining can have a disadvantageous effect on the frictional behavior, norcan the porous layer of the friction face close to the surface with thelower resin content have a disadvantageous effect on the settingbehavior. This leads to the consequence that in comparison with thestate of the art overall higher resin contents can be employed withouthaving to fear any reduction of the coefficients of friction.

[0006] Different methods can be employed to reduce the resin content forachieving a higher porosity in a surface layer of a friction liningwhose fabric has been saturated partly with liquid resin and wassubjected to a pressing pressure during the hardening of the resin. Onepossibility is that the resin is partly mechanically removed again inthe zone of the friction face after the hardening. This mechanical resinremoval at least partly uncovers the surface fibers of the fabric andremoves locally bound resin layers, which leads to an advantageousstructured friction face which as a result of its structuring isprovided with the porosity needed for draining off the lubricating film.The mechanical removal of the resin can be achieved by a brushing of thefriction face. It is also possible grind out the resin from the zone ofthe friction face or to use sandblasting for this purpose.

[0007] In order to reduce the resin content in a surface layer of thefriction face it is not necessary to mechanically remove the resinretroactively. It is also possible to suck off the resin during thepressing of the impregnated fabric from the surface region of thefriction face, e.g. with the help of a suction film which is placed onthe fiber layer saturated with resin prior to the hardening of the resinand is subjected to a pressing pressure jointly with the fabric, so thatthe resin which is still sufficiently capable of flowing is pushed fromthe layer adjacent to the suction film into the pores of the suctionfilm. After the pressing process and the hardening of the resin theresin saturated suction film can be drawn off from the friction face,whereby the released surface layer of the friction lining shows aconsiderably lower resin content than the remaining friction lininglayer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The subject matter of the invention is shown by way of examplesin the drawings, wherein:

[0009]FIG. 1 shows a friction lining in accordance with the invention ina sectional top view;

[0010]FIG. 2 shows said friction lining in a sectional view along lineII-II in FIG. 1 on an enlarged scale, and

[0011]FIG. 3 shows a sectional view along line III-III of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] According to the illustrated embodiment the friction liningcomprises a fabric 1 made of carbon fibers in a linen weave, with thewarp threads being designated with reference numeral 2 and the weftthreads with reference numeral 3. Said warp and weft threads 2, 3 eachconsist of a plurality of filaments which are not twisted, however.After an impregnation of the fabric with resin, at least the frictionface 4 is substantially relieved in a surface layer h of resin, whichoccurs either mechanically or by sucking off by means of a suction film.In said surface layer h, which comprises a thickness of 0.002 to 0.050mm, preferably 0.003 to 0.005 mm, the resin content is between 0 to 12%.In the remaining layer zone of the fabric 1 the resin content, which isindicated in FIGS. 2 and 3 by the crosshatching, is between 40 and 70%,preferably between 45 and 60%. As a result of the low resin share in thesurface layer h, a surface structure is obtained which is advantageousfor the friction lining, both with respect to frictional behavior aswell as with respect to the guidance of the lubricating liquid.

[0013] It is understood that the invention is not limited to thearrangement of the illustrated friction lining. The friction liningcould be arranged in several layers, so that the fabric 1 is applied toat least one further layer, e.g. a layer of non-woven material. As aresult of said additional layer, it would be possible for example toinfluence the sound transmission properties or the heat insulation ofthe friction lining. Notice should be taken in this connection that thehigh resistance to heat of the preferably used carbon fibers of fabric 1allows a higher heat strain of the friction lining when as a result ofsaid higher heat burden the bonding of the friction lining with respectto the friction lining carrier is not endangered. The heat strain on thebonding layer 5 between the friction lining and the friction liningcarrier 6 can be limited through a heat-insulating intermediate layer.

[0014] The structure of the fabric 1 can be diverse, namely both withrespect to the employed fibers as well as the type of weave. Althoughvery different fibers can be used in special cases, highly modulararamide fibers with a length-related mass of 22 to 158 tex and glassfibers made of E-glass with a strength of 22 to 300 tex are the fibersof choice. Carbon fibers on the basis of polyacryl nitrile of highstrength are particularly suitable. Non-twisted fiber bunches with 1000to 6000 filaments, preferably 3000 filaments, are preferred. Favorablysuitable for the fabrics are linen, sateen or double milled twill weaveswith a mass per unit area of between 80 and 400 g/m², preferably 170 to250 g/m².

[0015] Suitable resins are both duroplastic materials such as epoxy,phenol, polyurethane or polyamide resins as well as thermoplasticmaterials such as polysulfones, polyether imides or polyether ketones.Out of all possible resins, duroplastic materials on the basis of epoxyor phenole resins have proven to be particularly suitable.

[0016] The treatment temperature during the impregnation of the fibersmust be chosen depending on the respective second order transitiontemperature, which should be higher than 120° C., preferably higher than140° C. It is understood that the employed resins can be provided,depending on the respective application, with different additivesserving various purposes, e.g. for influencing the viscosity orstrength.

[0017] In order to produce a friction lining in accordance with theinvention, a respective fabric 1 is impregnated at first with resin,namely with the help of a resin solution, a resin melt or a resin film.After a partial hardening of the resin, a suction film is applied to thelater friction face 4 in a preferred embodiment of the invention.Suitable suction films are especially fabrics made of polyester orpolyamide threads in a linen weave with a mass per unit area of 50 to120 g/m². The friction lining with the suction film is then subjected ina second treatment stage to a respective temperature treatment in orderto ensure a complete hardening of the resin. In said second treatmentstage, the friction lining can be held under a pressing pressure of 1 to10 bars for example. On drawing off the suction film saturated with theresin a major part of the resin is removed from the surface layer h ofthe friction lining. The resin removal can also occur without the use ofa suction film by brushing, grinding or sandblasting of the hardenedsurface of the friction lining.

Example of an Embodiment

[0018] A commercially available fabric made of carbon fibers (of highstrength, 3000 filaments) in linen weave with a mass per unit area of200 g/m² was impregnated with an epoxy resin on the basis ofbisphenole-A and a hardening agent on the basis of methylene dianiline.In the employed impregnating unit the solvent was eliminated and thefabric impregnated with the resin was partly hardened at a temperatureof 180° C. The fabric treated with resin in this manner had a mass perunit area of 377 g/m² at a second order transition temperature of lessthan 100° C. Thereafter a suction film made of polyamide fibers with amass per unit area of 65 g/m² was applied on the fabric, namely on bothsides, and the fabric with the suction films was subjected in a press toa pressure of 3 bars at a temperature of 160° C. during a period of 4hours. After the hardening of the resin, the suction films were drawnoff. As a result of the partial resin removal on the surface facing thefriction lining carrier, the bonding of the bonding layer between thefriction lining and the friction lining carrier can be improved.

[0019] The produced friction lining showed a mass unit per area of 345g/m² with a second order transition temperature of 140° C.

1. A friction lining for wet running, consisting of a fabric (1) whichcan be applied to a carrier (6) and is partly impregnated with resin,characterized in that the porosity of the fabric (1) impregnated withresin is higher in the zone of the friction face (4) by a lower resincontent in a surface layer (h) than in the remaining layer.
 2. A methodfor producing a friction lining as claimed in claim 1, with a fabric (1)being partly saturated with liquid resin and the resin being thenhardened preferably under a pressing pressure on the fabric (1),characterized in that the resin is partly mechanically removed after thehardening in the zone of the friction face (4).
 3. A method as claimedin claim 2, characterized in that the resin is brushed out of thefriction face zone.
 4. A method as claimed in claim 2, characterized inthat the resin is ground out of the friction face zone.
 5. A method asclaimed in claim 2, characterized in that the resin is removed from thefriction face zone by sandblasting.
 6. A method for producing a frictionlining as claimed in claim 1, with a fabric (1) being partly saturatedwith liquid resin and the resin being then hardened preferably under apressing pressure on the fabric (1), characterized in that the resin issucked off from the surface zone (h) of the friction face (4) during thepressing of the fabric (1).
 7. A method as claimed in claim 6,characterized in that the resin is sucked off in the surface zone (h) ofthe friction face (4) via a suction film which is placed on the frictionface and can be drawn off from the friction face (4) after the pressingprocess.